In GNSS outages, what is the role of the INS?

• A. It stops updating until GNSS returns.
• B. It measures atmospheric delays to correct GNSS.
• C. It provides external corrections via satellite to correct drift.
• D. It uses integrated accelerometer and gyroscope data to propagate position, velocity, and attitude, but it drifts over time without GNSS updates.

Answer: (D)

In GNSS outages, the INS provides a self-contained way to track motion by integrating data from accelerometers and gyroscopes to propagate position, velocity, and attitude. This dead-reckoning approach keeps the navigation going, but the accumulated errors from bias and noise cause the estimate to drift over time without GNSS updates. That combination—continuous propagation with growing drift in the absence of external corrections—is why the described role is the correct one. The other ideas don’t fit: the INS doesn’t stop updating, it doesn’t correct atmospheric GNSS delays, and it doesn’t provide external satellite corrections.